The present invention relates to a process for producing dialkali metal phosphates and, more particularly, to a process wherein dialkali metal phosphates may be produced by ion exchange using readily available starting materials.
Alkali metal phosphates are an extremely useful class of compounds, e.g., as fertilizers. While various methods have been proposed in the past for their production, they have not all proven to be completely satisfactory due to difficulties encountered in processing or to the high cost of the starting materials. For example, one known technique for the production of dialkali metal phosphates employs wet process phosphoric acid and an alkali salt such as sodium hydroxide as starting materials. Thus, when combined with the wet process phosphoric acid, the alkali metal salt effects neutralization and subsequent precipitation of an alkali phosphate compound. Although wet process phosphoric acid is a readily available and inexpensive starting material, the alkali salts typically required, such as sodium hydroxide, are far more expensive and thus limit the commercial practicality of the above-described process.
Since the desired product is a dialkali metal phosphate compound, it was often found advantageous to react the phosphoric acid with a divalent alkali metal compound such as potassium carbonate (K.sub.2 CO.sub.3). However, like the sodium hydroxide system described above, systems employing a divalent alkali metal salt such as potassium carbonate are also undesirable from an economic point of view due to their prohibitive costs.